488 



HISTORY OF 



systems in their oonfoimation : like the cetaceous tribes, they 

 have organs of hearing, and lungs ; like the spinous kinds, they 

 have gills, and a heart without a partition. Thus possessed ot 

 a twofold power of breathing, sometimes by means of their lungs, 

 sometimes by that of their gills they seem to unite all the advan- 

 tages of which their situation is capable, and drawing from both 

 elements every aid to their necessities or their enjoyments. 



This double capacity of breathing in these animals, is one of 

 the most remarkable features in the history of Nature. The 

 apertures by which they breathe, are somewhere placed about 

 the head ; either beneath, as in flat fish ; on the sides, as in 

 sharks ; or the top of the head, as in pipe-fish. To these aper- 

 tures are the gills affixed, but without any bone to open and shut 

 them, as in spinous fishes ; from which, by this mark, they may 

 he easily distinguished, though otherwise very much alike in 

 appearance. From these are bending cylindrical ducts, that 

 run to the lungs, and are supposed to convey the air, that gives 

 the organs their proper play. The heart, however, has but one 

 valve ; so that their blood wants that double circulation which 

 obtains in the cetaceous kinds ; and the lungs seem to be rather 

 as an internal assistant to the gills, than fitted for supplying the 

 same offices as in quadrupeds, for they want the pulmonary vein 

 and artery. 



From this structure, however, the animal is enabled to live a 

 longer time out of water than those whose gills are more simple. 

 The cartilaginous shark, or ray, live some hours after they are 

 taken ; while the spinous herring or mackarel expire a few 

 minutes after they are brought on shore. From hence this tribe 

 seems possessed of powers that other fishes are wholly deprived 

 of; they can remain continually under water, without ever taking 

 breath ; while they can venture their heads above the deep, and 

 continue for hours out of their native element. 



We observed, in a former chapter, that spinous fishes have 

 not, or at least appear not to have, externally any instruments 

 of generation. It is very difl^erent with those of the cartilagin- 

 ous kind, for the male always has these instruments double. 

 The fish of this tribe are not unfrequently seen to copulate ; and 

 their manner is belly to belly, such as may naturally be expected 

 from animals whose parts of generation are placed forward. 

 They in general choose colder seasons and situations than other 



